Weld Purging is the act of removing oxygen from the vicinity of a weld, before, during and after the welding of certain metals, such as stainless steel titanium and nickel alloys. An inert gas is used (usually argon), displacing the oxygen from the weld zone and therefore ensuring the metal does not come into contact with oxygen as it is heated, which could lead to oxidation and a loss of corrosion resistance properties.
For tube and pipe welding, it is proven very cost effective to restrict the area needed to be purged, making vast savings on time and inert gas costs. This is done using an inflatable tube and pipe purging system.
PurgExtra® has been developed, for purging tube and pipe joints from 1 – 24” diameter. This design features an extra gas purge hose to speed up the purging process to ensure that the cost of the product is paid for in just one weld.
Luke Keane, Technical Support for HFT®, the leader in Weld Purging Technology, said: “A PurgExtra® System is simply inserted into a pipe and positioned using RootGlo®, a material adhered to the centre of each System, allowing the welder to see the System clearly through the root gap.”
“The PurgExtra® System is then inflated with the inert gas. Once the dams are inflated, the gas will displace the oxygen within the pipe ready for welding. Each System is manufactured with a Weld Purge Monitor® connection, to ensure the oxygen level can be measured, giving precise oxygen values throughout the purging process.”
“The PurgExtra® Range allows the operator to purge at the recommended rates initially and then, when conditions are correct, to introduce the additional gas at high flow rates. This system is especially valuable for achieving the lower oxygen levels required for welding materials around 20 parts per million.”
When welding joints where interpass temperature control is necessary, PurgExtra® allows extra argon gas into the welding zone, helping to cool the weld zone dramatically. The extra gas also helps to remove the gases that are expelled by the outgassing, which occurs as the metal is being heated.
The extra gas flow will prevent these expelled gases from combining with the hot metal and oxidising, which would otherwise cause the metal to discolour and lose its corrosion resistance and possibly introduce defects that would cause loss of joint integrity.
PurgExtra® comprises two inflatable dams connected by a heat resistant, highly flexible gas hose that has the unique IntaCal® gas release system. IntaCal® allows the dams to be inflated correctly and then releases the inert gas to safely purge the space between the dams. The low profile IntaCal® Valve replaces the old fashioned, bulky complicated valves and eliminates the need to make adjustments to flow rates.
The highly flexible spinal hose between the inflatable dams allows the PurgExtra® Systems to be pulled or pushed easily around bends and elbows.
The innovative PurgeGate® Valve may be fitted to the PurgExtra® Systems as an accessory, to protect the inflatable dams from bursting due to accidental over pressurisation.Heat Resistant Covers are also available for PurgExtra®, which fit onto the inflatable dams and allow operation with pre-heated and post-weld heat-treated pipe joints where the temperatures might reach 760°C.